The axial piston pump/motor is one of the most important power components and executive components in the hydraulic system, is widely applied in the industrial, agricultural, coal mine, military and other hydraulic systems, and is one of the two most widely used hydraulic components in modern hydraulic components. Meanwhile, due to the complicated structure of the axial piston pump/motor and the high requirements on the manufacturing technique and the materials, it is one of the hydraulic components with high technical content.
In recent years, with the rapid growth of China's economy and the development of materials, manufacturing, electronics and other technologies, in the process of industrial modernization and large-scale urbanization, the demand for axial piston pumps/motors is great in the field of engineering machinery, plastic machinery, metallurgy, machine tools and agricultural machinery. Thus, the axial piston pumps/motors still require constant technological innovations and structural improvements.
The piston shoe pair is one of the key friction pairs of the axial piston pump/motor, and is the direct bearer of the oil pressure in the piston cavity, which is extremely easy to become worn and fail. Therefore, the underside of the piston shoe must maintain the necessary lubrication state, and form a certain thickness of the oil film to ensure the liquid lubrication, so as to prevent the piston shoe from directly contacting the swash plate. The lubrication oil film should not be too thin, which is easy to lead to wear or failure. The lubrication oil film should not be too thick, which will reduce the volumetric efficiency of the piston pump, and even fail to establish the pressure adequate to the load. By means of the spring force, the main hydraulic pressure and the depressurized hydraulic pressure within the damping hole, the piston shoe pair structure of the traditional axial piston pump/motor forms a hydrostatic back-up and enable the pressing force to be slightly larger than the separating force, so as to ensure that the piston is pressed tightly on the oblique plane of the swash plate. The existing axial piston pump/motor presses the retainer plate through the spring on the transmission shaft, and the retainer plate presses the piston shoe and the piston, resulting in complicated force on the retainer plate and the higher fault rate.
The Chinese patent application No. 201510092027.2 discloses electromagnetic preloading piston shoe pair used in an axial piston pump and a motor, including a piston and a swash plate. One end of the piston abuts the surface of the swash plate through a piston shoe. The rear surface of the swash plate is provided with a boss. The boss is wound by coils. The coils are electrically connected to an external alternating current power supply. The patent utilizes the electromagnetic force to provide the preload force, which effectively solves the problem that the traditional piston shoe pair of the balanced-type multi-ring axial piston pump or the double-side driving piston motor has difficulty in designing, and optimizes the structure of the balanced-type multi-ring axial piston pump or the double-side driving piston motor. However, the following problems still need to be solved.
First, the electromagnetic force enables the piston shoe pair to attach on the swash plate by means of attractive force. When the oil film thickness decreases, the electromagnetic force increases, and the oil film thickness can only be maintained by its stiffness, thereby increasing the difficulty of maintaining the stable oil film thickness.
Second, the electromagnetic force distribution is not ideal enough, and the electromagnetic force fluctuates greatly along the circular motion direction of the piston shoe pair, which is adverse to the stable operation of the piston shoe pair.
Thirdly, the electromagnetic force is used in a single way, and only adsorbs the piston shoe, which fails to adapt the force condition of the piston shoe in the complicated operating process of the axial piston pump/motor, and fails to improve the wear situation of the bearing surface of the piston shoe.
In the cases of the above-mentioned problems, it is necessary to propose new structures and new technical means to further improve the working performance of the magnetic piston shoe pair.